^ people prefer the sound and looks of the 5".
it can be a pain to install and does not offer any more performance than a 4".
personal preference really. watch a load of videos and see which one you like better. for me the drone is a deal breaker
my 01 is pretty loud in the cab, but when you hook a load up that will make the dmax work it is very loud, if i was to pull things long distance then i would want a muffler or go down to 4inch... friend has an 04 reg cab with 4inch str8 and mines also an regular cab w/5inch str8.. mine is much louder inside and out, mine has alot deeper tone. idk if its cause he has a programmer and i dont but you can hear his turbo alot more than mine, and all he has in an edge and cai, i got cai and profab intake horn and his is still louder, but then again, mine is alot louder in the cab....and 06 DW LYY, thats a hole different deal, my 06 with 5inch str8 is very quite inside the cab and while cruising, my lb7 is at least 2 times louder in the cab with the windows up